This is true - but all your solo time counts - as does all of your solo time after you receive your SP certificate. In reality, there are 15 dual hours that you need to make up with a PPL CFI as you transition from SP. And since you have another 20 hours to meet the 40 hours minimum - it is fairly easy to do (long night xcountry, instrument nav, radio nav, towered airport ops) . If you are current and comfortable in your plane, it will be an easy transition.
Since there are very, very few cfi-s only instructors out there - and they are not likely to be doing beginning primary instruction - it's mostly a non-issue.
ExperimentalAviator wrote:If the CFI is a PPL CFI the training time and time after licensing can count to get a PPL... if the CFI is a SP CFI the time from training and after does not count to a PPL